Jellyfish are taking over the oceans: Population surge as rising acidity of world's seas kills predators

Scientists say the number of jellyfish are on the rise thanks to the increasing acidity of the world’s oceans.

The warning comes in a new report into ocean acidification – an often overlooked side effect of burning fossil fuel.

Studies have shown that higher levels of carbon dioxide in the atmosphere doesn’t just trigger climate change but can make the oceans more acid.

A jellyfish floats in the Mediterranean sea on the west coast of the Spanish island of Mallorca

Since the start of the industrial revolution, acidity levels of the oceans have gone up 30 per cent, marine biologists say.

The new report, published by the UN Environment Programme during the Climate Change talks in Cancun, Mexico, warns that the acidification of oceans makes it harder for coral reefs and shellfish to form skeletons – threatening larger creatures that depend on them for food.

The decline in creatures with shells could trigger an explosion in jellyfish populations.

The report, written by Dr Carol Turley of Plymouth University, said: ‘Ocean acidification has also been tentatively linked to increased jellyfish numbers and changes in fish abundance.’

Jellyfish are immune to the effects of acidification. As other species decline, jellyfish will move in to fill the ecological niche.

Populations have boomed in the Mediterranean in recent years. Some marine scientists say the changing chemistry of the sea is to blame.

Studies have shown that clown fish – the species made famous by the movie Finding Nemo – find it harder to navigate through more acidic waters.

A Clownfish on the reef in Raja Ampat Islands, West Papua province, in Indonesia. The fish is particularly susceptible to rising acidity

They are also less likely to avoid predators, and may activity seek them out, scientists have shown.

Test on laboratory fish have found that more acidic water rewires their brains, turning them into fish with a death wish.

The report says acidification may push overstressed oceans into disaster with far reaching consequences the billions of people who rely on fish as their main protein source.

The effects of extra carbon dioxide may be greater in colder waters such as the North Sea and north Atlantic, the report says.

The damage to corals and shellfish could affect the whole food chain – hitting species such as salmon which feed on smaller shell building animals.

‘The basic chemistry of sea water is being altered on a scale unseen within fossil records over at least 20 million years,’ the report said.

Oceans are naturally alkaline – and had a pH level of about 8.2 in 1750. Since the industrial revolution, the acidity has increased by 30 per cent.

As more carbon dioxide enters the oceans it produces carbonic acid.

As the acid breaks down it makes sea water less alkaline and more acidic.

‘If we continue at this rate, the ocean pH will decline by a further 0.3 by the end of this century, an unprecedented 150 per cent increase in ocean acidity,’ the report states.

‘This rate of change has not been experienced for around 65 million years, since the dinosaurs became extinct.’